This invention relates to the use of solvents in the finish application of solvents in the finishing operation of spun polyester yarns and the method for the production of spun polyester yarns where the finish application eliminates circumferential stress cracking.
Heretofore, spun polyesters produced by conventional processes including melt spinning, finishing, winding and draw twisting, have been susceptible to defects within the structure of each individual filament. These defects include circumferential stress cracking in each filament which seriously weakens the oriented strength of the filaments and the yarn produced therefrom.
In the conventional production of spun polyester, the melt spinning process where the filaments are formed through the spinnerette is followed by the application of a finish coat to prepare the filaments which are wound together for subsequent draw twisting. This finishing operation has typically employed various proprietary emulsion compositions which lubricate the filaments in preparation for draw twisting under elevated temperature and drawing conditions. An emulsion such as Nopcostat, a proprietary solution produced by the Diamond Shamrock Corporation has conventionally been prepared in proper concentration in an aqueous solution.
With the use of aqueous solutions, circumferential cracks in the filaments of the spun polyester yarn appear after the yarn has been melt spun during production time lags. These cracks seriously weaken the spun yarn before their orientation in draw twisting, such that draw twisting cannot be performed on these defective filaments, even though the conditions of melt spinning, production lag time, and draw twisting are well within conventional requirements. Therefore, a different solvent system is necessary for the emulsion that lubricates and finishes the filaments following melt spinning prior to draw twisting. Use of a different solvent could minimize or eliminate circumferential stress cracks in the spun polyester yarns.